The purpose of this project is to investigate the immunoregulatory properties of malignant lymphocytes. We are currently determining the helper and suppressor activity of neoplastic T-cells from patients with acute lymphoblastic leukemia and the Sezary syndrome. We are also attempting to characterize normal and neoplastic T cells on the basis of certain surface membrane markers directed by binding of the Fc-piece of IgM and IgG, and other markers detected by antibodies raised in animals.